The field of this invention is that of metal-oxide-semiconductor (MOS) integrated circuits, and the invention relates more particularly to an improved MOS input buffer for use in such a circuit.
Microprocessors implemented in NMOS integrated circuit technology are typically proposed for use in automotive control applications to meet the speed, complexity and cost requirements of such applications. However the LED or vacuum fluorescent display means and PMOS display driver means which are usually proposed for use in such automotive applications to meet the requirements of cost and sunlight conditions and the like have input requirements which are typically not compatible with the voltage levels of the logic signals provided by such NMOS microprocessor means. That is, conventional input buffer means are not adapted for use between the NMOS microprocessor and the associated PMOS circuit means. For example, the input signals provided by the NMOS microprocessor are referenced to the drain supply voltage so that a conventional input buffer utilizing a grounded source enhancement device and a saturated load with the Beta ratio adjusted for input voltage levels is found to be inappropriate. Similarly, known input buffer means utilizing differential amplifier means are found to provide very little gain and are also considered inappropriate. Accordingly relatively expensive CMOS buffer means and the like have been proposed for use to permit the preferred microprocessor, display, and driver means to be employed together in automotive control applications.